Patient compliance with drug therapy for diabetic nephropathy

William Clark and colleagues were clearly sensitive to the effects of patient compliance in their study of the cost-effectiveness of angiotensin- converting-enzyme (ACE) inhibitor therapy for diabetic nephropathy.1 This highlights 3 important assumptions regarding compliance that require further clarification.

First, it was assumed that noncompliers lose renal function at the same rate as patients in the placebo arm of a diabetic nephropathy trial comparing the effects of ACE inhibitors and placebo.2 It would seem unlikely that patients taking up to 80% of their ACE inhibitor (the definition Clark and colleagues offered for noncompliance) would lose renal function at the same rate as those taking none. The rate at which noncompliers lose renal function should have been subjected to sensitivity analysis.

Second, the authors based their analysis on the results of a patient- interview study3 in which 34% of patients stated cost as the primary barrier to compliance. To suggest that 34% of patients would be noncompliant for this reason is a major assumption. A recent observational study of persistence with antihypertensive therapy suggested that the relationship between drug cost and compliance was less clear.4 The more expensive ACE inhibitors were in fact associated with higher persistence rates. Thus, when one is evaluating the implications of noncompliance, factors other than drug costs must not be ignored.

Finally, provincial drug coverage may not have had as much impact as assumed because a proportion of patients already have the cost of their medications covered through private insurance. Before ACE inhibitor coverage becomes standard practice, we propose that the effect on compliance of providing medications free at the point of delivery should be more thoroughly assessed. If such studies confirm that compliance improves significantly, then consideration could, in fact, be given to developing a national pharmacare program, whereby cost-effective medications, such as ACE inhibitors for diabetic nephropathy, would be provided free to all Canadians.

Competing interests: None declared.